Incumbent agency W Communications parted ways with Lidl in July, having been appointed as the supermarket's first UK PR agency in February last year.
Headland is handling corporate PR for Lidl. The agency's remit also includes financial PR and public affairs, as well as senior communications advice and press office support in the UK.
Headland partners Simon Burton and Lucy Legh will lead the account. Burton said: "Lidl has taken the UK grocery market by storm, and as the brand moves to become a major player, we're excited to be part of that journey."
Good Relations, meanwhile, has been appointed to a consumer PR brief. The agency will work alongside Lidl's in-house marketing team to amplify the supermarket's 'Big on Quality, Lidl on Price' brand slogan.
Agency director David Wiles, who will lead the account, said: "There are so many more great stories to tell about Lidl and we will be working closely with Lidl's fantastic in-house team to make sure we help the brand achieve even more success in the near future."
Last year the retailer said it planned to invest £1.5bn on expansion by 2019, with 280 stores slated to open in London alone. It has also entered the US this year, and plans to open 100 stores by summer 2018. Lidl also recently overtook Waitrose as the UK's seventh biggest supermarket.